Previously cup-shaped plugs with perforated or slotted bottoms have been used in the vents adjacent the cavity in a drag of a core box; however, each plug had a diameter never greater and often less than the width of the slot or groove in the cavity, not to mention being contoured to the cavity. Therefore, in order to obtain adequate venting for fast production operations, the number of vents and bolt holes which could be formed in the drag became insufficient as well as weakening the drag, thus limiting the core box operation.
Generally speaking, the core box involved produces sand cores for castings. This core box has a cope (top) and drag (bottom) which form a mold cavity for forming the sand core. Usually the sand is injected into the cope and most of the air in the mold cavity is forced out through vents in the cavity spaced away and preferably remote from the injection of the sand. The vents thus are usually in the drag, but may also be in the cope, including the sides of the cavity for pull jacks to form undercuts. In order to prevent the sand from passing through the vents, each vent adjacent the cavity is provided with a plug having a cylindrical cup-shape whose bottom is filled with perforations having openings less than the minimum diameter of the sand grains making up the core, so that sand will not escape or plug the perforations.
The important feature of this invention is forming these plugs and their vents with diameters at least 50% larger, and preferably twice or more times the width of the slots or grooves in the cavity where the vents are to be located. Furthermore, the perforated bottoms of the cup-shaped plugs also may be and preferably are contoured to fit and continue the contour of the cavity, slot or groove where they are located. Although this structure does not take advantage of all of the apertures in the enlarged cup-shaped plug, it more than compensates for the perforations which do not open into the cavity by providing perforations along the length of the slot and/or groove, as well as also up any contoured sides thereof. Since the diameter of the vent and plug are greater than the width of the cavity slot where the larger vents are located, it is essential that the end of the plug conforms with the portion of the cavity in which it is located. The perforations in the plug may comprise holes or slots which may be parallel or formed into different configurations.
The plugs are held in place by sleeves in the vent apertures, which sleeves contact the peripheral or cylindrical flange forming the rim of the cup of the plug. These sleeves also are of sufficient length to hold the plugs in proper alignment with the cavity. The other and outer end of these sleeves may be held in place by the head or a washer on one or more adjacent bolts, preferably two, which heads or washers overlap the outer end of the sleeves. Furthermore, because of the space necessary for these bolts and washers to hold the sleeves in place, there can only be a certain amount of vents or holes placed in the bottom or sides of the drag or mold without weakening it, i.e. by the plurality of vent holes and bolt holes therein. Thus fewer and larger and more spaced apertures for vents are employed, not only to maintain sufficient strength in the mold, but also increasing the amount of air that can be vented at one time. Since the diameter of the vents and their cups are greater than the width of the slot, groove or end of the cavity, the space taken up by one large vent and/or its contoured plug allows much more air to be vented at a time, than two or even three or more small prior art plugs in smaller vent holes.